Storm jib - smaller is better. These days a bight coloured band (or completely orange) is the normal colour. Make sure the tack fitting is a quick connect & release snap fitting that can be easily operated with one hand, not a shackle. Sheets should be sewn on permanently. High cut along the foot is important to allow green water to escape underneath it. You would probably set it with your cars as far forward as possible.
The methods of folding it is very important - bear in mind you may well be deploying it when things are getting very hairy. You will typically concertina the sail & heavily tie it with wools to stop it flailing in the breeze. Once you connected the tack, hanks & halyards, run the sheets, you will break the wools & deploy the sail when you pull it up.
Any decent sailmaker will be familiar with this, there is probably even a youtube video showing what I'm talking about.
Good luck with it.

Poods